华北及邻区地壳上地幔三维速度结构的地震走时层析成像  

Tomographic Imaging of P and S Wave Velocity Structures Beneath North China and its Vicinity

作　　者：王志铄[1] 王椿镛[1] 曾融生[1] 王溪莉[1] 

机构地区：[1]中国地震局地球物理研究所

出　　处：《CT理论与应用研究（中英文）》2008年第2期15-27,共13页Computerized Tomography Theory and Applications

基　　金：科技部科技基础性资助项目(华北精细结构探测);中国地震局重点项目(中国大陆数字壳幔结构);国家自然科学基金(40334041;90814001)

摘　　要：利用华北及邻区475个地震台站的区域地震走时资料,反演了该地区的地壳上地幔三维P波和S波速度结构。地震走时的计算用近似弯曲射线追踪方法,三维速度模型的反演用LSQR算法。用检测板方法对走时数据进行成像分辨率分析,结果表明反演模型在水平方向上以0.5°×0.5°的节点分布,垂直方向上以1km、10km、25km、42km、60km为节点作网格划分是合理的。研究区域内,秦岭—大别造山带两侧的华北块体与扬子块体有不同的速度异常特征:华北块体地壳速度结构复杂,而扬子块体则相对简单。华北块体地壳内存在较明显的低速异常,而扬子块体则正常或高速异常。自中新生代以来华北块体地壳经历挤压到伸展的强烈变形,而扬子块体相对稳定。华北块体的构造活动依然强烈,表现为频繁的地震活动。华北地块地壳速度结构的主要特征是:①主要构造带(如燕山构造带、太行山山前构造带、汾渭构造带、郯庐断裂带以及秦岭一大别构造带)位于地壳上地幔的低速或高低速过渡区内;②在唐山及附近地区25 km、42 km和60 km深处连续的低速异常,可能意味着上地幔热的物质上涌,到达上地壳的下部后停止上升过程。The regional travel-time data from 475 seismic stations in the North China and its vicinity were used to inverse the P and S velocity structures of the crust and uppermost mantle.The pseudobending ray tracing algorithm was used to calculate the travel times.The large and sparse system of observation equations is solved by using the LSQR algorithm.According to the checker-board tests,reliable inversion results were obtained for a parameterized model with grid size of 0.5°by 0.5°in the horizontal directions and 5 nodes of 1,10,25,42 and 60 km in depth.The Yangtze Block and the Sino-Korean Block are located in two sides of the Qinling-Dabie orogenic belt.The differences of velocity structure between two Blocks are that lower velocity anomaly exists in most part of the Sino-Korean Block,while velocity distribution is normal in the Yangtze Block.This indicates that the Yangtze Block is relative stable,and the Sino-Korean Block is still active,where strong earthquakes have frequently occurred.Main features of the'velocity structure in the Sino-Korean Block are that major tectonic belts (such as Yanshan uplift,Taihangshan piedmont fault belt,Tanlu fault belt,and Qinling-Dabie orogenic belt)are located in the low velocity areas or the transition zone from low velocity area to high velocity area in the crust and upper mantle.In the Tangshan earthquake area,low velocity anomaly commonly exists at the depth of 25 km,42 km and 60 km,which may imply that the hot material in upper mantle upweUs,and then stops to the lower part of upper crust.

关 键 词：华北地区 地震层析成像 地壳和上地幔速度结构 分辨率 

分 类 号：P315.2[天文地球—地震学]